134 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 17 



Type: Holotype is represented by Gray's original specimen in the 

 Herbarium of the British Museum of Natural History, London. 



Type locality: Vancouver Island, British Columbia, Canada. 



Mexican distribution: Pacific Baja Calif. — ^Widespread and 

 variable in size and branching along the whole coast from Punta Des- 

 canso at least to Isla Magdalena. In the northern part of the range it 

 favors protected and rather well-insolated tide pools. On Isla Guadalupe 

 it occurs as a small slender form with relatively sparse, long, flexuous 

 branches. 



In a specimen from Punta Baja (Dawson 1212) the tetrasporangia 

 were observed to be only once divided to produce bispores. 



Key to the Mexican Species of Amphiroa 



1. Segments ( as seen from below) with a more or less distinct, 



thick midrib, at least in part A. foliacea 



1. Segments normally without an externally distinguishable mid- 

 rib 2 



2. Upper segments mostly cylindrical or nearly so (only 



occasionally with some strongly compressed parts) . . 3 

 2. Upper segments mostly distinctly complanate ... 6 

 2. Upper segments mostly compressed, but sometimes in part 



nearly cylindrical 9 



3. Genicula unizonal; annulations prominent; segments mostly 



200-300 /A in diameter . . . . A. annulata and var. 



3. Genicula multizonal; annulations not prominent; segments 



250-1300 IX in diameter 4 



4. Segments 250-450 ju. in diameter, crooked, with constric- 

 tions at the genicula A. taylorii 



4. Segments mostly 350-1300/a in diameter, generally 

 straight, smooth, without conspicuous constrictions at the 

 genicula, or these only between coarsest segments . . 5 

 5. Segments mostly 1000-1300 /x in diameter; genicula more or 



less prominent A. subcylindrica 



5. Segments 350-550 /a in diameter; genicula obscure, usually not 

 visible from the surface . . . A. drouetii (in part) 

 6. Upper segments (2-) 3-4 mm. wide, more or less dor- 



siventral A. dimorpha 



6. Upper segments 1.5-2.5 mm. wide, not recognizably dor- 



siventral 7 



